I heard that the duration of patent in the US was recently raised from 17 years from when the patent issues to either 17 years from when the patent issues or 20 years from when the patent is applied for (whichever is longer? whichever is shorter ? Does one term always trump the other if the patent issues ? I don't know.)
As it happens, the some commentators claim to find a "tendency to require a somewhat greater degree of originality in order to accord copyright in a musical arrangement". Nimmer on Copyright 2.05[C],2-57 (2nd Edition, 1978).